The exemplary embodiments of the present invention relate to a liquid crystal display device and a projection display apparatus.
Liquid crystal display devices are used as optical modulation devices of projection display apparatuses, such as a liquid crystal projector. In the liquid crystal display devices, a liquid crystal layer is interposed between a pair of substrates. An electrode to apply an electric field to the liquid crystal layer is formed inside the pair of substrates. An alignment film to control an alignment state of liquid crystal molecules is formed inside the electrode. Image light is formed on the basis of variation in the alignment of the liquid crystal molecules at the time of applying a non-selection voltage and at the time of applying a selection voltage.
In the projection display apparatus employing the related art liquid crystal display device, the contrast ratio of a projected image is at most 1:500, which is still smaller than the contrast ratio of 1:3000 in the projection display apparatus employing a mechanical shutter such as DLP (registered trade mark) technology using DMD (digital micromirror device). This results from a viewing angle characteristic of the liquid crystal display device. Originally, the source light which enters the optical modulation device of the projection display apparatus is not a complete parallel light. Since the liquid crystal display device used as the optical modulation device has an entry-angle dependency, this causes reduction of the contrast ratio of the projected image.
Therefore, in order to compensate for the entry-angle dependency of the liquid crystal display device, an optical compensating plate is employed. The optical compensating plate hybrid-aligns discotic liquid crystal molecules showing a negative birefringence (see, for example, Japanese Unexamined Patent Application Publication No. H8-50206 and “Introduction Lecture 11 for Liquid Crystal Display: Viewing-angle Enlargement Technique of TFT-LCD with Discotic Optical Compensating plate”, Liquid Crystal, Japan Liquid Crystal Society, Vol. 6, No. 1, p 84-92, Jan. 25, 2002, by Hiroyuki Mori). As seen in the normal direction, the optical compensating plate has a fast axis and a slow axis due to the hybrid alignment. Accordingly, the optical compensating plate has a phase retardation in the normal direction.
FIG. 13 is a graph illustrating a viewing-angle dependency of the phase retardation in the optical compensating plate described in Japanese Unexamined Patent Application Publication No. H8-50206. It can be seen from FIG. 13 that the phase retardation when the viewing angle to the optical compensating plate is 0°, that is, the phase retardation in the normal direction of the optical compensating plate, is about 40 nm. Examples where the phase retardation in the normal direction of the optical compensating plate is 70 nm and 80 nm are disclosed in Japanese Unexamined Patent Application Publication No. H9-15587.
In addition, a first optical compensating plate is disposed at the outside of the substrate at the light-entry side in the liquid crystal panel and a second optical compensating plate is disposed at the outside of the substrate at the light-exit side. The first optical compensating plate and the second optical compensating plate are disposed such that the fast axis direction (that is, the X axis direction which is an alignment control direction of the discotic liquid crystal and is indicated by Arrow 71 in FIG. 5 which shows an exemplary embodiment of the invention) as seen in the normal direction of the respective optical compensating plates is approximately equal to the alignment control direction of the alignment film in the corresponding substrate. Since the alignment control directions of the respective substrates in the liquid crystal panel are approximately perpendicular to each other, the alignment control directions of the optical compensating plates are approximately perpendicular to each other.